A typical friction or journal bearing used in rock bits, as shown for example in U.S. Pat. No. 4,178,045, has opposed cylindrical surfaces formed on stepped diameter sections of the bearing pin and cone. The surfaces oppose and engage one another as the bit is turned on bottom under load applied by the drill collar string to which the bit is attached. Due to heavy loads that are imposed on the bearings during normal drilling operations, significant amounts of friction and heat are generated which limit the bearing life. Of course it is desirable that the bearing life equal or exceed the life of the cone cutting structure, so that the drill string will not have to be tripped to change the bit before the cutting structure has been worn out.
The usual approach to design of bearings of this type has been to maximize the nominal bearing surface areas within the confines of the structural integrity of the rolling cutters or cones, with the objective of presenting larger and more dispersed contact areas at the load-bearing points. Such bearing structures are susceptible to early damage by contaminant particles or by small particles of metal dislodged as a result of the wearing process which adhere to the hearing surfaces and greatly accelerate the wearing process toward catastrophic failure. There is a need for trapping such particles so that they do not remain between rubbing bearing surfaces. Yet another shortcoming of prior structures is that the plain bearing surfaces have not been sufficiently lubricated to provide for maximum bearing life in the somewhat hostile environment in which drill bits are used. Although helical grooves in solid bearing members have been suggested heretofore, such structures have limited compliance and are easily worn and damaged at areas of localized concentration of stress and localized high temperatures.
A general object of the present invention is to provide a new and improved friction or journal bearing structure of the type described having a significantly improved bearing life.
Another object of the present invention is to provide a new and improved rock bit journal bearing that includes open areas for trapping debris particles so that such particles do not interfere with movement between opposed bearing surfaces.
Another object of the present invention is to provide a new and improved rock bit journal bearing constructed and arranged to provide large spaces adjacent to engaged bearing surfaces for the storage of lubricant and supply thereof to contacting bearing surfaces to reduce wear.
Another object of the present invention is to provide a new and improved bearing structure which functions to pump lubricant as one bearing member rotates relative to the other to provide a continuous supply of lubricant to bearing contact areas.
Another object of the present invention is to provide a new and improved rock bit journal bearing constructed and arranged to provide a wiping action of one bearing member over the other to evenly distribute lubricant and thereby reduce wear.
Still another object of the present invention is to provide a new and improved journal bearing structure having spaced bearing surfaces formed by wound wire capable of accommodating some degree of misalignment of parts.